Technologies concerning femtocell Base Stations (BSs) supporting indoors or shadowing areas that are not supported by macro cells have recently been defined. A femtocell BS is an ultra small, low-power indoor BS and a femtocell is the coverage area of a femtocell BS. Although a femtocell is conceptually similar to a pico cell, a femtocell BS is an advanced BS relative to a pico cell BS, in terms of functionality. The femtocell BS is a small cellular BS connected to a broadband router, for transmitting data to a backbone network of a mobile communication service provider via a Digital Subscriber Line (DSL) link or the like. The term “femtocell” is a combination of the term “femto” representing 1 divided by ten followed by 15 zeroes and the term “cell” representing a service coverage unit of mobile communications. The use of femtocells increases communication quality through efficient conjunction between a wired link and a wireless link. As a femtocell transmits mobile communication data directly from a BS to an exchange without the intervention of an indoor relay, a communication service provider may reduce a frequency load, while minimizing network configuration cost.
There are largely two types of femtocell BSs, CSG femtocell BS and Open Subscriber Group (OSG) femtocell BS. An OSG femtocell BS is accessible to all MSs, whereas a CSG femtocell BS is accessible only to MSs of a group to which a CSG ID of the femtocell BS is allocated.
An open access mode, a closed access mode, and a hybrid access mode are defined for operations of a CSG BS.
When a femtocell BS is in the open access mode, it is accessible to all users. An MS performs initial entry to the femtocell BS without comparing a CSG Identifier (ID) received from the femtocell BS with a user CSG list of the MS. The user CSG list lists CSG IDs of femto cells accessible to the MS, managed by the MS.
In the closed access mode, the femtocell BS is accessible only to specific users. Hence, the MS performs initial entry to the femtocell BS only if a CSG ID received from the femtocell BS is present in the user CSG list of the MS.
As is implied from its appellation, the hybrid access mode allows for both the open and closed access modes.
There may exist a femtocell accessible MSs with a first CSG ID and MSs with a second CSG ID. How to allocate a CSG ID to this femtocell and which MSs to notify of the CSG ID become issues to be solved.
FIG. 1 illustrates a scenario in which Company B moves into a building with Company A already located therein and a CSG ID should be allocated to a femtocell that workers of both Company A and Company B should access.
Referring to FIG. 1, when only Company A is located in the building, workers of Company A can access Femtocell A and Femtocell B, and the CSG IDs of Femtocell A and Femtocell B are both CSG ID 1. Then Company B moves into the building and workers of Company B should be able to access Femtocell C, Femtocell D and Femtocell B. Specifically, Femtocell B covers an area which all workers of Company A and Company B should be able to access, such as a lobby.
Accordingly, there exists a need for a method for allocating a CSG ID to Femtocell B and notifying an MS of the allocated CSG ID.